With a high number of murders occurring in a few days, the L.A. police department was overwhelmed. Rushing from one murder scene to the next, Bosch was not able to give any case the time and thorough investigation it needed. Prematurely forced to leave the site of the seemingly random murder of Anneke Jespersen, a Danish journalist, Bosch knows the case will probably never be solved.

Apparently in the United States on vacation after covering the first Gulf War, Jespersen was near Los Angeles when the riots broke out. It seems she hurried to L.A. to get a story she knew she could sell to her European editors. But how did this war-savvy photojournalist end up dead, her photos stolen, on her first night in town? It looks like a random act of violence, but a few things hint to old-dog Bosch that it might have been more personal.

Surrounded by fires and gunshots, forced to move on to yet another murder site, Bosch looks at the dead woman, still lying in a dirty suburban alley, and whispers, "I'm sorry."

Two decades later, with the 20th anniversary of the riots approaching, LAPD knows the media will once more be asking about all the unsolved murders from the riots. It would look good if a few are solved. Bosch, now in the Open-Unsolved Unit - cold cases - gets a new chance to look at the Jespersen murder. This time he means to give it the full force of his attention. But the trail, always faint, has now disappeared entirely. Or, maybe not.

Taking one of the most popular and consistently exciting cops in contemporary crime fiction back 20 years is author Connelly's way of celebrating the publication of his first novel, which also starred Bosch, in 1992. Since then Bosch - full name, Hieronymus Bosch - has appeared in 19 of Connelly's 25 novels, usually as the main character. These days most of Connelly's books about Bosch or L.A. "Lincoln Lawyer" Mickey Haller (Bosch's half-brother) make their way to No. 1 on the best-seller lists.

Bosch attacks this new case the same way he always attacks a case, biting down and refusing to let go until he feels justice has been done, even when his own superiors seem to be against him. This time, someone way up the department ladder has realized that if Bosch solves this case, while other L.A. riot murder cases go unsolved, it will create bad press for the historically racist L.A. police. Most of the murder victims during the riots were African-American; Jespersen was white. Attempts to force Bosch off the case create the background tension that is a hallmark of Bosch stories.

Despite the seemingly insurmountable problems created by lack of evidence, dead participants and two decades of change, Bosch keeps digging at every loose thread until, finally, a few begin to unravel. Jespersen, it turns out, was not in the United States on vacation, and her L.A. story may not have been about the riots. If he can discover her real purpose, maybe he can uncover her killer.

"The Black Box" features most of the aspects that have made Connelly's Bosch novels among the most intriguing and surprising crime novels on the market: misdirection, countless obstacles thrown in Bosch's path by friend and foe, the detective's determination to be the advocate for a forgotten victim and Bosch's own internal conflicts and issues. Like Henning Mankell's famous Swedish detective, Kurt Wallander, Bosch has struggled with alcohol and other problems, including an often disastrous private life. And he has had major anger issues.

The Bosch books have more product placement than a Bond movie in the form of Bosch's (Connelly's?) favorite bars, restaurants, taco stands and jazz clubs, all prominently, and sometimes inelegantly, inserted. Then there are the constant references to Connelly's current beloved jazz heroes (his website, michael connelly.com, includes a section on the music in his books). Many a fan has discovered new jazz favorites in a Bosch novel. In "The Black Box," the cop drives around listening to "Unreleased Art," a multivolume set of Art Pepper recordings.

The novels have their own form of prose music, the equivalent of haunting, nonmelodic, powerful jazz, never pretty but with a harsh beauty. In the past few Bosch novels, perhaps since "Nine Dragons," the music has seemed, to this reader, a bit forced.

"The Black Box" is minor Bosch, still better than most crime stories, but a long way from the usual standard. As often happens with series that go on a long time, Bosch of late has become a little paint by the numbers. The story is good, the twists surprising, but the prose seem heavy-footed and Bosch's anger with the world seems rote.

Recently, Connelly gave Bosch's troubled life a bit of love and peace with a daughter the hero is crazy about. The result is the kind of domestic happiness antithetical to what makes Bosch fascinating. The chapters featuring father-daughter interplay interrupt the story's flow and are bland.

The book climaxes with a rush of plot and last-minute action, and here, too, it's not quite what we have come to expect. While reasonably satisfying and exciting, it is implausible and ends in B-movie melodramatics. Perhaps after 20 years, Connelly should give Harry Bosch a well-deserved rest and let Mickey Haller carry the masthead awhile.

Louis B. Parks, a freelancer living in the Texas Hill Country, is a former Chronicles features reporter and film writer.